1. Field of the Invention
The present invention relates to an imaging apparatus having a solid-state imaging device and a correction unit that corrects defective signals contained in a plurality of image signals output from the solid-state imaging device.
2. Description of Related Art
A CCD solid-state imaging device includes a plurality of photoelectric conversion elements, a plurality of vertical transfer section (VCCDs) where charges generated at the plurality of photoelectric conversion elements are read out and transferred in a vertical direction, a horizontal transfer section (HCCD) where the charges transferred through the plurality of VCCDs are transferred in a horizontal direction orthogonal to the vertical direction, and an output section that outputs an image signal corresponding to the charges transferred through the HCCD.
The VCCDs include charge transfer channels formed in a silicon substrate and a plurality of electrodes formed above the electrode transfer channels through a gate insulation film. FIG. 4 is a sectional view of a VCCD, which is 8-phase driven, having four electrodes correspondingly to one photoelectric conversion element. The reference character “C” designates a charge transfer channel, and the reference characters V1-V8 are electrodes provided above the charge transfer channel. The electrodes V1, V5 are respectively assumed serving also as read electrodes to read out a charge from the photoelectric conversion element. In the VCCD, It is assumed that potential wells P1, P2 are respectively formed under the electrodes V1, V2 and V5, V6 so that charges generated at the photoelectric conversion element are read in the potential wells P1, P2 and then transferred in the arrow direction in FIG. 4. Here, it is also assumed that a defect exists in the charge transfer channel of the VCCD and the defect causes a potential failure 21, the potential of which is suddenly deepened, in the potential well P2 under the electrodes V5, V6.
When charges are transferred through the VCCD having the potential failure 21, charges are to build up there each time passing over the potential failure 21, and thus the number of charges read out from the device is decreased. For example, provided that the potential failure 21 has a capacitance of 10 charges and the amount of charges read out from a photoelectric conversion element is 5 in average, the charges obtained from two photoelectric conversion elements build up at the potential failure 21. No signal output is available based on the charges stored in the potential failure 21. Consequently, an image 30, obtained by imaging a pure white subject, is blackened only at two pixels as shown in FIG. 5A. These are defective pixels 22.
Meanwhile, provided that the potential failure 21 has a capacitance of 10 charges and the amount of charges read out from a photoelectric conversion element is 1 in average, the charges obtained from the photoelectric conversion elements build up at the potential failure 21. No signal output is available based on the charges stored in the potential failure 21. Consequently, an image 30, obtained by imaging a pure white subject, is blackened only at ten pixels as shown in FIG. 5B. These are defective pixels 22.
The average amount of charges read out from a photoelectric conversion element changes in accordance with an ISO sensitivity of the device. The number of defective pixels increases with the increase of the ISO sensitivity while the number of defective pixels decreases with the decrease of the ISO sensitivity. Namely, the number of defective pixels is in proportional relationship with the ISO sensitivity.
There is known a technique to correct a defective pixel with use of its surrounding pixels. However, where defective pixels differ in number with a change of ISO sensitivity as noted above, devising is required for the manner of correction. No effective corrections have been available in the related art. For this reason, where there is a defective pixel resulting from a potential failure as noted above, it is a practice to determine that an solid-state imaging device having such a potential failure is unacceptable not to be shipped to the market.
JP-A-2004-88209 is a document related to a digital camera having a function to correct defective pixels. In this digital camera, whether or not correction of defective pixel is performed is selectable in accordance with an ISO sensitivity of the digital camera. However, this document does not describe how to correct a defective pixel resulting from such a potential failure as mentioned above.